JP2002524598A - Foamed polypropylene sheet having improved appearance, apparatus and method for producing the same - Google Patents

Abstract

  (57) [Summary] Expandable polypropylene comprising a polypropylene resin having a D1238L melt flow rate of about 0.5 to about 30 g / 10 min, and a method and apparatus for extruding a rigid foamed polypropylene sheet having an improved surface appearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION

The present invention relates to polyolefins, and in particular to improved expanded or foamed compositions comprising propylene polymers. Furthermore, the present invention relates to an apparatus comprising an improved extrusion die and a method for extruding a rigid or semi-rigid foamed polypropylene sheet having an improved surface appearance. The foamed polypropylene sheet according to the present invention can be easily thermoformed into a shaped article. These articles are particularly useful in the manufacture of rigid and semi-rigid packaging, trays, plates, containers and other articles useful for food serving applications.

[0002] Polystyrene is widely accepted as being useful for food provision applications due to its good hardness and shape retention, and is easily molded and thermoformed as a foamed sheet. However, polystyrene articles suffer damage at low service temperatures,
Generally fragile and has low chemical resistance. In the field of food service and packaging, there has long been a search for alternatives that do not have these undesirable properties.

[0003] Polyolefin resins are widely known for their ease of manufacture and have found a great variety of uses. In recent years, great efforts have been made to develop rigid expanded or foamed polyolefin sheets as a substitute for foamed styrene, particularly suitable for use in food serving applications. Polyethylene resin has medium strength, high durability and 10
A softening point in the range of 5-140 ° C. Such resins are suitable for foam extrusion and provide an attractive low density thermoformable foam sheet having good low temperature properties. A foamed polyethylene sheet and a molded foam article exhibiting an excellent appearance,
It is easily manufactured from low density polyethylene resins and finds wide applicability in various packaging and food serving applications. However, polyethylene foam is generally soft, flexible, and has poor heat resistance. Thus, acceptance is limited for food serving applications that require hardness and are intended for contact with hot food.

[0004] Propylene polymers, or polypropylene resins, have received particular attention for their good heat resistance and mechanical properties, and have various structural and decorative applications in the manufacture of molded parts such as appliances, household articles and automobiles. There are supplied polypropylene-based resin formulations that meet the requirements of the US. Shock-absorbing polypropylene and elastomeric ethylene propylene copolymers have been found in automotive applications, including interior trim, and exterior parts applications such as shock absorbing dashboards, grill components, rocker panels, and the like. Polypropylene resin has heat and chemical resistance, withstands a wide range of environmental exposure, and has metal stamping.
), Which are easily molded at a much lower cost and provide rust protection, ie, they do not corrode and exhibit impact resistance even at low temperatures.

[0005] A number of methods for making expanded polypropylene have been disclosed and described in the art.
For example, U.S. Patent No. 5,18, JJPark et al., Which is incorporated herein by reference.
There is a method disclosed in Japanese Patent No. 0,571. Park et al.'S patent is generally around 0.0
Regarding extrusion of polypropylene to provide a foamed sheet of low density in the range of 4~0.44g / cm ^3.

[0006] On the surface of the extruded foamed polypropylene sheet, a layer can be generally found consisting mainly of crystalline polypropylene (PP). This surface layer or jacket is important for imparting appearance and surface hardness. The thickness and crystallinity of the PP surface layer will depend to some extent on extrusion conditions, including die temperature and cooling rate, and on annealing. The Park et al. Patent relates to extrusion of polypropylene to provide a foam sheet having a smooth surface envelope and a uniform cell structure. According to Park et al., High melt strength, high melt strength with a specific combination of molecular and rheological properties, including bimodal molecular weight distribution, to produce foamed sheets with a smooth surface envelope and uniform cell structure It is necessary to use elastic polypropylene together with highly branched minor components. The patentee is a low density extruded foam sheet using conventional or common polypropylene resin, and furthermore, a comparative example characterized as a less branched polypropylene resin having a monomodal molecular weight distribution, Generally, it has an uneven sheet surface and an uneven microcell structure, indicating that it is not suitable for commercial use.

[0007] The surface of the extruded foamed polyolefin sheet is generally, in particular, foamed high density AB
Lack of smooth, glossy, uniform and substantially scratch-free surfaces observed on extruded expanded styrene sheets, including S-sheets. For example, surface irregularities are typically imparted when extruding a foamed polyethylene sheet, and the lack of uniformity in cell structure and on-surface distribution is more readily visually apparent due to the transparency of the unfilled polyethylene. Detectable surface roughness (ie, irregularities can be detected tactilely) can be reduced during the extrusion process by contacting a low melting temperature polyethylene sheet with a polishing roll to provide a smoother, more uniform surface. Can give. The remaining surface imperfections are primarily visible density fluctuations and are generally uniformly distributed, giving a generally generally acceptable or marbled surface appearance.

[0008] Rigid expanded polypropylene sheets obtainable by methods currently known and practiced in the art have some disadvantages in surface appearance properties. Characteristically, foamed polypropylene sheets extruded in a conventional manner using conventional or common polypropylene resins are regularly arranged in the form of staggered bands extending along the length of the sheet in the machine direction. With spaced or corrugated markings. In lightweight, low-density foams obtained from conventional polypropylene resins, especially soft and flexible foams having a density of 20 lb / ft ³ (0.3 g / cm ³ ) or less, these bands will reduce the corrugated sheet. It has the form of regularly spaced wavy or sinusoidal curves that form. Bands or corrugations become less noticeable in rigid foam sheets, especially at higher foam densities, appearing as surface scratches or cosmetic defects in the form of linear, bulky surface depressions along the machining direction.

[0009] It is more difficult to sufficiently smooth the surface roughness of an extruded sheet using a resin having a higher melting temperature using a polishing roll. In addition, defects and visible density variations seen on the surface of extruded foamed polypropylene sheets are often not evenly distributed over the entire surface, and are generally common even for tactilely smooth sheets. Completely visible. In higher density foams with the desired hardness for the manufacture of food service articles, defects are characterized by readily visible variations in opaque surface gloss, which may include surface voids, foam, streaks, and uneven color. It appears more frequently as a pattern of staggered linear bands of high and low foam density applied. Such flaws will not significantly affect the mechanical properties of the foam and will generally not affect the function of the article ultimately made from such foam. But,
In consumables, food packages, and the like, these visible surface defects and associated surface flaws are highly undesirable and, as a result, limit the application of rigid foamed polypropylene sheets in industry.

[0010] The coextrusion of multilayer sheets having a solid skin and a foam core has been disclosed in the art and surface appearance encountered during the manufacture of various conventional foam sheet materials, including sheet materials formed from polystyrene and ABS. It is widely used to solve the above problems. A foamed core sheet with a glossy non-foamed surface layer formed from the same resin or a different resin will have improved resistance to surface peeling and cutting and will have a better appearance. A stiffer skin makes the foam structure rigid and allows for a lighter and thinner structure while achieving maximum bending stiffness. Foam sheet coextrusion methods are well described in the art for use with various resins such as polystyrene and ABS. Recently, a method using coextrusion of a multilayer foam sheet containing a polyolefin including polypropylene has been disclosed. The coextrusion method has the disadvantage of requiring more expensive feedblocks, dies and associated processing equipment with more complex designs, thus complicating the operation,
The production cost of such a foamed sheet is increased.

[0011] Thus, conventional common polypropylene resins having an attractive, defect-free surface appearance, reducing visible surface defects and associated surface flaws required for acceptance in the food serving and packaging industries There is a need for a rigid foamed polypropylene sheet comprising the same and a polypropylene composition comprising conventional common polypropylene resins suitable for use in the extrusion of such foamed sheets.

[0012]

Summary of the Invention

The present invention relates to the production of rigid foamed polypropylene sheets with significantly improved surface appearance. In particular, the present invention relates to a propylene polymer, a crystallization nucleating agent, a foam nucleating agent and a foaming agent used for producing a rigid foamed polypropylene sheet having a high density of about 0.45 g / cm ³ or more and excellent strength and heat resistance. And an improved expandable polypropylene composition comprising: When extruded using an improved extrusion apparatus and a die in accordance with the additional teachings described herein, the resulting high density foamed polypropylene sheet will have the surface bands commonly found in extruded high density rigid foam sheets, It is characterized as having a more uniform cell structure, with an improved surface appearance with significantly reduced corrugations and associated visible flaws. Thus, the present invention can also be characterized as an improved extruded rigid foamed polypropylene sheet.

The rigid foamed polypropylene sheet according to the present invention has a low average surface roughness uniformly distributed over the entire surface of the foamed sheet, and the corrugations and surface bands are substantially eliminated. Upon molding or thermoforming, the foamed sheet of the present invention provides a rigid or semi-rigid article having an improved surface appearance while maintaining a good balance of mechanical properties, including stiffness and toughness. Thus, the present invention can be further characterized as a molded article having an improved appearance comprising expanded or expanded polypropylene.

[0014]

[Description of preferred embodiments]

A particular advantage of the invention described herein is that it uses a wide variety of commercially available polypropylene resins without reviving certain resin grades and blends,
It is to provide a high-density foam sheet having an excellent surface appearance. The polyolefin compositions useful for extruding thermoformable rigid foamed polypropylene sheets according to the present invention are preferably substantially linear polypropylene homopolymers or propylene and small amounts of alpha-olefins up to 6 carbon atoms ( About 30 wt% or less, more preferably about 30 wt%
20 wt% or less). The polymer may be syndiotactic or isotactic, but preferably uses an isotactic polypropylene homopolymer having an isotactic index of preferably 0.85 or more, more preferably 0.92 or more. The polymer melt flow index is ASTM D
From about 0.3 to about 10, preferably from about 1.0 to about 4.0 g / 10 min, as determined according to 1238. Such polymers can be readily prepared by a variety of well-known catalytic polymerization processes, including those using catalysts based on Ziegler-Natta and metallocene catalysts.

[0015] Substantially linear polypropylene resins having a wide range of extrusion grades, film formation, essentially monodile molecular weight distribution and the required MFR, and no significant branching, are readily available, almost Has been found to be useful in accordance with the teachings of the present invention to provide a foamed sheet having an improved surface appearance.

According to the teachings of the prior art, it is generally believed that a high melt strength resin formulation is required to continuously extrude foamed polypropylene with good cell structure and acceptable surface appearance. The prior art also discloses that in order to use them, certain formulations (including specific grades of propylene resin having rheological properties including a defined molecular weight and a bimodal molecular weight distribution including highly branched minor components) ( formulation). Mixed compositions having the required melt strength have also been formulated with modified polypropylenes, such as, for example, crosslinked or highly branched olefin polymers with certain polymerization additives.
Although these particular resin grades and resin formulations have also been found to be useful in the practice of the present invention, foamed sheets having an improved surface appearance are readily available from common grades of polypropylene. That is, it can be easily produced from a propylene polymer resin having a monomodal molecular weight distribution and being less branched, and such a specific resin composition is not required.

As disclosed and described in the art, the expandable polypropylene composition will further include a blowing agent and a crystallization nucleating agent. Blowing agents are well known and may be of the type widely used in the manufacture of extruded polystyrene and the manufacture of polyolefins, including polypropylene, such as azodicarbonamide, diazoaminobenzene, azo-bis-isobutyronitrile and Organic blowing agents containing these analogous substances, and inorganic blowing agents containing, for example, ammonium carbonate, sodium bicarbonate and the like can be mentioned. Physical blowing agents such as nitrogen, carbon dioxide and other inert gases, chlorofluorocarbons (CFCs), HCFCs
Agents that undergo a phase change from liquid to gas during the foaming process, such as low boiling alcohols, ketones and hydrocarbons, are also known for their use and may be useful in the practice of the present invention. Can be found. The blowing agent may further include one or more additives to lower the decomposition temperature.

The amount of blowing agent to be used depends on the properties of the blowing agent and the desired density of the expanded polypropylene, and will be selected according to practices well understood by those skilled in the resin forming arts. Generally, blowing agents are traded in the form of concentrates. The concentrate is
Active foaming agent will be added to the formulation in a range of about 0.2 wt% to about 10 wt%, preferably about 0.4 wt% to about 5 wt%, based on the total weight of the formulation. The amount of a physical blowing agent, such as a liquid blowing agent and an inert gas, required to provide a desired expansion density can be readily determined according to common industry practices.

As described in the art, crystallization nucleating agents increase the number of crystallization nuclei in molten polypropylene, thus increasing the rate of crystallization and promoting crystallization from the melt. Solidifies the resin at higher temperatures. In general, non-nucleated polypropylene begins to crystallize around 120 ° C. and has a crystallization rate peak around 110 ° C. The nucleated polypropylene resin may begin to crystallize at a temperature on the order of about 135 ° C to 140 ° C and have a peak around 130 ° C. Nucleated resin is
Rapidly solidifies with improved melt strength and reduces sagging of extruded foam sheets. The crystallization nucleating agent is generally present in an amount of about 0.1 wt% to about 0.5 wt%, preferably about 0.05 wt% to about 0 wt%.
It can be used in amounts of .3 wt%. Agents disclosed in the art and used to improve the rate of crystallization include sodium organophosphates such as bis (4-tert-butyl-phenol) phosphate, sodium benzoate, and aromatics. Examples thereof include a mixture of a monocalboxylic aromatic acid or an aliphatic polycarboxylic acid and a silicate or an aluminosilicate of an alkali metal or an alkaline earth metal. The use of sodium organophosphate as a crystallization nucleating agent is described in the art, for example, in U.S. Pat.
No. 833.

Other agents disclosed in the art to improve the melt strength of polyolefins include sorbital, dibenzylidene sorbital and related compounds.
These agents have been described in the art as networking agents and crystallization nucleating agents for use in modifying the low shear melt viscosity and low shear melt strength of polyolefins. However, it will be appreciated that reticulated binders are not effective for providing high density rigid foamed polypropylene sheets according to the present invention.

[0021] Additional modifiers and additives for the expandable polypropylene composition are also disclosed and described in the art. Such modifiers and additives include lubricants, coolants and / or desiccants, refractories, heat and UV stabilizers, antioxidants, antistatics, and the like, and are commonly used in the art. It can be used in a corresponding amount. Those skilled in the art will recognize that such additional modifiers and additives are selected to avoid undesired reactions with the resin, blowing agent and nucleating agent, and that these agents are in accordance with normal practice in foaming resin compounding and forming techniques. Will be used at a level appropriate to its function and purpose.

[0022] The improved foamable polypropylene composition of the present invention will further include a foam nucleating agent. The foam nucleating agent creates foam sites, has a desirable effect on cell size, minimizes the occurrence of large cells and open cell structures, and thus provides a particularly attractive, uniform and high quality foam sheet. The use of a foam nucleating agent in combination with a crystallization nucleating agent further improves foaming processability and melt rheology, and desirably enhances the important mechanical and thermal properties of the foamed sheet, especially hardness or stiffness.

[0023] The foam nucleating agent used to form the improved compositions useful in foam sheet extrusion according to the present invention can be prepared from various inert solids disclosed in the art as being useful as foam nucleating agents. Choices may include citric acid and sodium bicarbonate or other alkali metal bicarbonates, talc, silicon dioxide, diatomaceous earth, kaolin, polycarboxylic acids and their salts, and mixtures of titanium dioxide. Other inert solids disclosed in the art for these purposes have also been found to be suitable. The nucleating agent preferably has an average particle size in the range of about 0.3 to about 5.0 microns (μm), and is about 5% by weight of the total formulation, preferably about 0.01 to about 5% by weight, more preferably about 0.5 to about 5% by weight. Present at concentrations up to 2 wt%. At higher concentrations, the cell structure becomes undesirably small and the nucleating agent tends to agglomerate during processing.

[0024] Various compounding and mixing methods are well known and commonly used in the art.
Most of them are suitable for mixing and compounding the expandable polypropylene compounding components. Conveniently, the resin together with the stabilizer and further additives and modifier components is not heat-sensitive and may be in any form of powder, pellets or other suitable form,
The resin components are mixed and melt compounded using a high shear mixer, such as a twin screw extruder, at a temperature effective to melt the resin components to obtain the desired homogeneous mixture. The heat-sensitive component of the formulation, including the blowing agent, may be physically mixed with the powdered or pelletized resin using conventional dry mixing methods just prior to sending the mixture to the extruder. It is common practice in the art to plasticize in a compounded extruder and to feed additive and modifier components to the molten composition through ports in the extruder. Downstream addition to the melt will also be found to be particularly useful for foam sheet extrusion. Here, a physical blowing agent in gaseous form is used.

[0025] Thermoformable polyolefin foam sheets having improved surface appearance along with high modulus, operating temperature and thermal insulation are provided by using an improved coathanger-type foam sheet extrusion die according to the present invention. It would be obtained by extruding the expandable polyolefin composition.

The method of extruding the foamed sheet is generally performed through a plasticizing step and a mixing step using an extruder having one or a plurality of extruders which may be a single screw extruder or a twin screw extruder. The polypropylene resin and additives are mixed to provide a mass of melt foamable resin at the entrance of the sheet extrusion die. Preferably, the extrusion die is a coat hanger type sheet extrusion die. Here, the entrance extends in the form of a relatively wide and vertically narrow cavity, i.e. a coat hanger type plenum that is long in the horizontal or transverse direction (Y-axis) and relatively narrow in the vertical direction (Z-axis). Exist. The resin flow direction, ie, the machining direction, is also called the extrusion axis (X axis). The plenum extends along the width of the die, i.e., along the Y-axis, and is in fluid communication with an outlet port or mouth that forms a slit defined by the die lip. The molten foamed resin entering the die through the entrance spreads across the width of the die by the plenum, passes between the die lips, and through the exit port or die exit in a molten or semi-molten state as a continuous sheet. Get out. The extruded sheet then cools and solidifies, for example, by cooling the foam by passing it through a roll stack to finish the sheet. Different roll and take-up speeds may be used to stretch the foamed sheet and orient the crystalline polypropylene to achieve the final morphology and thickness as a sheet.

Referring now to the drawings, FIG. 1 illustrates a typical coat hanger die for extruding a thermoplastic sheet, generally indicated by the reference numeral 10, which is represented by the first or dashed line. It includes a lower half 1 and a second or upper half 2. When combined in opposing relation, the upper and lower halves form a cavity 3. The molten foam resin
It enters through the entrance 4 and flows into the plenum 5 in the form of a coat hanger. Plenum
5 is a melt well where the molten resin is passed through a preland passage 6
When flowing to 7, the molten resin is spread uniformly across the width of the die. Adjustable choke means (not shown) may be included to control the resin flow and
The remaining differential pressure may be made uniform by 7. The molten resin continues to pass through a flat extrusion passage or die land 9 defined by opposing spaced surfaces of lower die lip 11 and upper die lip 12 and exits the die via outlet opening 8 to form a sheet.

The die body may include passages for heating and cooling, and further include a clamp
It should be understood that fastening means and means for incorporating the die into the extruder are required but have been omitted from the drawing for clarity.

FIG. 2 shows a prior art sheet extrusion die 20 including an assembled upper half 21 and lower half 22, a cavity 23 defining them together, and an upper die lip 14 and a lower die lip 15. I have. As described above, the molten foamed resin is extruded from the extruder means (not shown) under pressure into the die cavity 23 in fluid communication with the outlet opening 28.
Up to the inlet 24. Flowing into the coat hanger plenum 25 and blocked by the narrowing of the cavity in the preland passage 26, the melt stream is spread by the plenum 25 across the width of the die and fills the melt receiver 27. The molten resin is further conditioned by adjustable choke means 61, flows from the melt receiver 27, passes through an extrusion passageway or die land 29 and exits through the outlet opening 28 as a continuous foam sheet.

Either or both die lips 14 and 15 may be fixed or removable, as desired. As shown in FIG. 2, the lower die lip 14 is made removably and is provided with a plurality of bolts or other suitable fastening means.
, While the upper die lip 15 is fixed. To adjust the gap between the die lips at the outlet opening 28, the upper die lip 15 may be provided with adjusting means 62, as shown.

In the conventional extrusion die as shown in FIG. 2, the opposing surfaces of the upper die lip 14 and the lower die lip 15 that are brought into contact with the molten resin flow are plane, substantially parallel, and have substantially uniform height. Alternatively, it defines a smooth extrusion passage or die land 29 having a thickness. The continuous foam sheet that exits the die lip in a molten or semi-molten state expands further when it exits, and at least the temperature of the outer skin falls below the crystallization temperature, and when it solidifies, it reaches its final thickness and surface state. Will have sufficient internal pressure to reach.

To complete the finishing of the extruded foam sheet, conventional sheet extrusion methods generally employ a finishing roll stack (not shown) that may include chilled rolls to further cool the sheet. Optionally, a cooling means, such as an air flow, may be provided at the outlet port to quickly cool the surface of the emerging foam sheet. Initially shaped by the outlet opening 28, the final thickness of the foam sheet depends on the part of the cooling means used, the roll gap in the finishing roll stack and the ratio of extrusion speed to winding speed, and Can be selected depending on the desired stretching of the sheet and the orientation of the crystalline polypropylene component of the foamed sheet.

Referring to FIG. 3, which illustrates an embodiment of the improved sheet extrusion die according to the present invention, FIG.
An improvement over the prior art is in the improvement of the die lip 16, which provides a die land 39 having a wide hole going downstream along the extrusion axis from the vicinity of the melt receiver 37 to the outlet opening 38 together with the upper die lip 17. It will be seen that this provides an expansion zone 65. The molten foam flowing from the melt receiver 37 of the die 30 enters the expansion zone 65, expands under the effect of the pressure drop, and exits the outlet opening or die port as a continuous foam sheet. Expansion of the foam to a predetermined thickness is almost complete in the die land. By avoiding further significant swelling after exiting the die port, surface bands, corrugations and similar surface markings can be significantly reduced and eliminated entirely. Such defects are commonly found in extruded foam sheets using a conventional extrusion die without the expansion zone, for example, as shown in FIG.

It will be appreciated that it is desirable to assist the cooling of the foam sheet in the expansion zone 65 to accelerate crystallization. For this purpose, cooling means may be included in the upper die lip 16 and the lower die lip 17 near the outlet opening 38. Using a finishing roll, stretching roll, or the like, the process can be completed and the foamed sheet can be finished to its final thickness and shape, if desired.

Referring to FIG. 4 showing another embodiment of the present invention, a lower die lip 18 is attached to a die land 49.
And by modification of the upper die lip 19, a wide hole toward the downstream side along the extrusion axis,
That is, an inflation zone 65 may be provided, so that inflation of the foam to a predetermined thickness is substantially completed within the die land.

The geometry of the extrusion die is designed to meet specific conditions characterized by the rheology of the melt. Determining a particular value for the variation in die gap geometry in the above-described embodiment is that the die opening or die gap unduly limits the desired final foam product thickness factor as well as many other factors. Will be easily understood. One of ordinary skill in the art will determine the appearance and uniformity of a sheet product as a modifier of the die lip according to the present invention when determining the exact die geometry and dimensions and process throughput rates to produce a given product. It can be seen that it has been improved as described.

In defining a complete and improved method of making a foamed polypropylene sheet according to the present invention, consideration is given to the operating parameters including die gap or opening and die land or extrusion passage length and throughput speed, product size and bulk density. Must. The geometric parameters are not determined independently of the operating parameters.

Referring to FIG. 5, which is shown as a partially enlarged view of the die land of FIG.
Wide bore 49 is further seen that characterized by the height or thickness t ₂ in the minimum height of the height or thickness t ₁ and a narrow point or die land passage at the die outlet opening 48. Generally, the initial thickness of the extruded foam sheet depends on the outlet opening
It will be substantially determined by the height of 48. Accordingly, the thickness t ₁ is determined depending on whether the die is intended for a product of a thin and dense expanded film sheet or a product of a thicker foamed sheet. When the thickness is small, it is about 0.01 inch (0.025 cm). May be greater than 0.2 inches (0.5 cm) when larger, and even larger if the die is used to make foam boards or the like. To be suitable for the production of a foam sheet having an acceptable surface appearance according to the invention, the geometry is the difference (t ₁ -t ₂ ), ie the height or thickness t ₁ at the outlet opening 48 and the minimum within the die land. may be those differences are partly characterized by the height or thickness t ₂ at the height position will be within the range of from about 0.004 to about 0.10 inches (0.01-0.25cm). Alternatively, the geometry of the die land to produce a suitable foam sheet beyond the range of interest is determined by the height or thickness t ₁ of the passage at the outlet opening 48 and the minimum height t ₂ within the die land. It may be characterized by the ratio t ₁ / t _2, may range from about 2 to about 5.

The geometry of the die land suitable for producing the foam sheet according to the invention is further defined by the length l of the die land or passage 49 determined from the downstream edge of the melt receiver 47 to the outlet opening. ₁ and may be characterized by a length l ₂ of the wide part forming the expansion zone 65. In general, the length (l ₁ -l ₂ ) or Dineland 4
The length of the first narrow portion of the die land, defined by the difference between the length of 9 and the length of the expansion zone 65, will be in the range of about 0.125 to about 0.75 inches (0.3-1.9 cm).

These parameters are for an improved extrusion die design to meet the requirements for manufacturing extruded foam sheets according to the present invention over a wide range of manufacturing volumes, including the embodiment shown in FIG. In general.

In operation of the foam sheet extruder, the upper die lip adjusting means may be used to change the die gap, ie, the narrower opening, and further control the sheet thickness. The improved sheet extrusion die according to the embodiment of FIG.
Prior to expanding to a total height t ₁ of the die, it may be operated using a selected winding speed to remove the foam sheet from the die, and the operator can operate the minimum height and maximum height within the holes of the expansion zone 65. adjust the sheet thickness greater than a limited range by t ₁ and t ₂ to be able to maintain.

The expanded polypropylene sheet extruded using the improved extrusion die according to the present invention has an improved surface appearance with little or no surface bands, corrugations or similar surface markings, and is evenly dispersed It may be characterized as having a low level of surface roughness as provided and providing a pleasing cosmetic appearance to the foam sheet.

The surface roughness and the uniformity in the surface roughness are determined by image analysis,
It provides a numerical basis to distinguish quantified and acceptable foam sheets from unacceptable foam sheets. In particular, uneven surfaces reflect light non-uniformly, while areas of the smooth surface are more reflective and appear as white or light gray in gray-scale micrographs of the surface. Areas containing defects such as voids and notches that form corrugated bands scatter light, and thus appear as dark gray or black in grayscale micrographs. When digitized using a computerized image analysis method and translated into a binary black / white image, the average surface roughness of the foamed sheet is related as the amount of black in the binary image and is expressed as a fraction per total surface area. Will be determined.

The uniformity of the distribution of the roughness over the surface may also be determined from the micrograph again by image analysis. The uniformity of the surface roughness is related to the variation of the roughness over the area of the micrograph, considering even areas of the image, averaging the roughness of each area,
Determined by obtaining the standard deviation. The most uniform surface is the surface with the lowest standard deviation.

As reflected by the low standard deviation in roughness over the area tested, foamed sheets having a low average surface roughness uniformly distributed over the surface generally have an acceptable appearance. It is considered to have.

The improved sheet extrusion die according to the present invention may further be found to be useful for the extrusion of non-foamed polypropylene sheets, or for the extrusion of multilayer foamed sheets or foamed core sheets, and Foam extrusion dies having a die land with an expansion zone in accordance with the teachings include an improved annular die and are formed in alternate shapes, in shapes suitable for extrusion of foam boards and planks, and improved. It will be appreciated that it may be formed by profile extrusion of a shaped foam structure having a roughened surface appearance.

The foamed polypropylene sheet obtained using the improved extrusion die of the present invention comprises:
Surface bands, corrugations or similar surface markings will have an improved surface appearance with less or no surface markings. The methods and processes of the present invention and the compounded and improved extrusion dies used in the present invention provide for the production of improved expanded polypropylene over a wide range of densities, including low density flexible foams for packaging use. , And 1
It can be used in the production of foamed polypropylene planks and boards having a thickness of 4 inch (0.6 cm) or more, and a thickness of 1 inch (2.5 cm) or more. According to the present invention, there is substantially no bands or similar surface defects, from about 10 mils (0.25 mm) to about 250 mils (6 mm);
Preferably, the thickness ranges from about 20 mils (0.5 mm) to about 80 mils (2 mm) and from about 0.4 g / cm ³ to
About 0.8 g / cm ^3, preferably about 0.45 g / cm ³ ~ about 0.8 g / cm ^3, more preferably about 0.5 to 0.75
A rigid foamed polypropylene sheet having a foaming density in the range of g / cm ³ is produced.
The hardness of the high-density foamed sheet of the present invention is generally reflected by the high tensile modulus of the foamed sheet in the range of about 150,000 psi (1000 MPa) or more, more preferably in the range of about 150,000 psi to about 300,000 psi (1000-2000 MPa).

The lower density foamed polypropylene sheet is more flexible and does not have the hardness required for hard food packaging applications and the like. Thus, the lower density foamed polypropylene sheet disclosed in U.S. Pat.No. 5,149,579 has a 10,000 to 50,000
It is characterized as having a modulus and modulus value in the range of 00 psi (70-340 MPa). At a foam density of about 0.8 g / cm ³ or higher, the foamed polypropylene sheet will not have the thermal insulation properties required in many applications.

A thin rigid foam sheet made according to the present invention will have good thermal insulation properties with a thermal conductivity in the range of about 0.08 W / m # K to about 0.15 W / m # K. Highly advanced foam sheets combined with good thermal insulation are useful in food serving applications where it is necessary to maintain the food above or below ambient temperature for some time, such as cups and similar hot or cold liquids. It would be particularly attractive and important in the manufacture of containers for handling. Foams intended for these uses will preferably have a thermal conductivity of about 0.14 W / m # K or less, more preferably about 0.11 W / m # K or less.

[0050] Foamed polypropylene sheets made from the polypropylene compositions improved according to the present invention can be used in conventional thermoforming operations to form rigid and semi-rigid articles. Typically, such articles are formed from foamed sheets having a thickness of 0.25 mm to 5 mm or more. Thermoformed articles typically range from 0.5 to 2 mm. In general, the foam sheet thermoforming process includes the steps of heating the foam sheet to a temperature at which it can be deformed under pressure or vacuum, supplying the softened foam sheet to a molding die, and cooling the foam sheet to form the mold. Forming a rigid or semi-rigid article having a shape. In order to avoid collapse of the foam structure of the sheet, the temperature used in the heating step is limited to a narrow range not exceeding the melting temperature of the resin. Since the processing window or temperature range for thermoforming, especially the upper temperature limit, can be conveniently evaluated by a thermochemical analysis process, a sample of the sheet can be measured using a thermochemical analyzer probe to determine the change in sheet thickness as a function of temperature. Heated while monitoring as. Upon reaching and exceeding the upper limit of the processing range, the thickness of the sheet is observed to decrease rapidly as the foam structure collapses and the probe penetrates the sheet. In general, extruded foamed sheets containing polypropylene can be processed with good retention of the foamed structure at temperatures ranging from about 130 ° C to about 145 ° C, with certain formulations having temperatures as high as 150 ° C while retaining the foamed structure. It can be seen that it can be processed by

In another aspect of the invention, the surface layer may be applied by a co-extrusion technique. Typically, top and bottom layers having a layer thickness: foam core thickness ratio of about 1: 1000, preferably 1: 2000 or more are used. Although an appropriate polypropylene polymer can be used, a propylene polymer having a composition similar to that of the foam core (excluding the foaming agent) is preferably used as the surface layer. Further, if desired, a barrier resin layer such as a polyethylene polymer or an ethylene vinyl acetate polymer may be added. The advantage of a coextruded surface layer is that it incorporates pigments or other specific additives to the surface layer. Since the amount of surface layer is much less than the foam core, the use of pigments or other additives is minimized. This can be an advantage in reusing articles.

The extruded foamed polypropylene sheet with improved surface appearance according to the present invention comprises
In addition to molded articles, it has applications for a wide range of physical shapes and forms. Rigid and semi-rigid foams, including molded and laminated products, not only have good physical properties and good resistance to chemicals at room temperature, but also over a wide range of temperatures and over long periods of time. Retains strength and good performance. Articles molded from the preferred foam compositions of the present invention have a significantly improved surface appearance and are particularly useful in food packaging where appearance and cosmetic considerations are particularly important for consumer acceptance. is there. Examples of these include plates, cups, trays and take-out food containers and home meal replacement products (home meal).
replacement items). Because these articles are made from propylene polymers having a relatively high softening point, they can typically be used in microwave ovens. Foam sheets and molded articles also have mechanical strength,
A wide range of applications can be found, such as weatherable articles and equipment components and medical applications where hardness and thermal insulation are important considerations, plumbing applications where resistance to hot and humid environments is particularly important, and safety equipment and protective gears. it can.

The present invention will be better understood by considering the following examples and comparative examples. However, the present invention is not limited to the following examples. In the examples, parts and% mean parts by weight and% by weight, unless otherwise specified.

[0054]

【Example】

The PP resin used in the following examples was obtained from Amoco gas phase method (Amoco Gas Ph
ase Process). The method is described in "Polypropylene Handbook" published in 1996 ("Polypropylene Handbook", Hanser Publications, NY).
On pages 297-298. "Simplified Gas-Phas," which was contributed to U.S. Pat. No. 3,957,4848 and Petrochemical Review, March 1993 (Petrochemical Review), the teachings of which are incorporated herein in its entirety.
e Polypropylene Process Technology ”.

[0055] The PP resin is initially provided in powder form. The resin powder may be used directly, or the blending and pelletizing may be performed first by strand extrusion using a mixed extruder, and then the strands may be cut. Pelletization may be completed according to a conventional method. For example, the dry resin may be dry-mixed with a stabilizing component and additives (if necessary) and supplied to a ZSK-30 twin-screw extruder. Good. The polymer extruded from a conventional die in water is cut to form pellets. PP resins are generally characterized by molecular weight. Measured values used to describe resin molecular weight include resin melt flow rate (MFR) in addition to resin viscosity. Generally, molecular weight is inversely proportional to MFR.

The component materials used in the following examples are as follows. Also, the following abbreviations are used. Polypropylene resin: PP-1; propylene homopolymer, powder, MFR = 2 g / 10 min PP-2; propylene homopolymer, powder, MFR = 1 g / 10 min PP-3; propylene homopolymer, pellet, MFR = 2 g / 10 min PP-4; Propylene-ethylene copolymer, pellet, MFR = 2 g / 10 min Crystallizing nucleating agent: Nucl-1; Sodium benzoate Nucl-2; Sodium organic phosphate, MARK NA- from Adeka Argus Chemical Company
Nucl-3 obtained as 11; dimethyldibenzylidene sorbitol, Milliken Chemical Company
Foaming agent obtained as Millad 3988 from FPE-50; 50 obtained as SAFOAM FPE-50 from Reedy International Corporation
Proper sodium bicarbonate-based blowing agent added as a wt% active concentrate
CF-40E; proper sodium bicarbonate based blowing agent added as a 40 wt% active concentrate obtained as BI CF-40E from BI Chemical Company H-40E; obtained as BI H-40E from BI Chemical Company A suitable sodium bicarbonate based blowing agent foam nucleating agent added as a 40 wt% active concentrate : talc; average particle size 0.8 micron, maximum available as Microtuff AG-609 and AGD-609 grades from Specialty Minerals Inc. Talc with a particle size of 6 microns In the following examples, the test methods used in evaluating the manufactured foam sheet include the following methods. Melt flow rate (MFR): determined by ASTM D1238, Condition L (230 ° C., 2.16 kg load) Density: determined according to ASTM D1622 Crystallization temperature (Tc) and melting point (Tm): substantially ASTM E Determined by differential scanning calorimetry in accordance with -793 Thermal conductivity: determined using the C-matics model TECM-DV instrument from Dynatech Corporation, according to test procedures issued by the manufacturer Tensile test: substantially ASTM Evaluation according to the procedure of D638-Evaluation of cell dispersion and size: This was performed by observing a cut surface obtained by microtoming the PP foam sheet with a scanning electron microscope (SEM). Sample sections were obtained along the transverse and machining directions. The cut sample section was placed on a SEM stub, covered with Au / Pd, and accelerated at 10 kV in secondary electron image mode of a Hitachi S-4000 scanning electron microscope.
Tested. The cell distribution is excellent, very uniform,
good, good, fair, poor, very poor
The evaluation was subjectively evaluated visually.

[0057]

Examples 1 to 6 In Examples 1 to 6 and Comparative Examples C-1 to C-3, a powdered propylene homopolymer resin (PP-1) having an MFR of 1.0 was blended to substantially form a foamed sheet. Extrusion was performed according to the following general procedure. The formulations are outlined in Table I below. Here, all components are given in weight percent based on the total weight of the formulation, with the balance of the formulation being PP-1. Examples 1 to 6 include a foam nucleating agent (talc) and a crystallization nucleating agent, and Comparative Examples C-1 to C
Formulation -3 appears to contain only a foam nucleating agent and no crystallization nucleating agent.

The indicated amounts of the additives other than the polypropylene powder and the blowing agent were dry-mixed in the indicated amounts, supplied to a ZSK-30-containing extruder, melt-mixed and extruded to form pellets. The resin pellets were dry mixed with the indicated amount of blowing agent and fed by gravity through a popper to a 2.5 inch (6.4 cm) single-screw NRM extruder with a 24/1 L / D screw with barrel and die heating. . The barrel of the extruder was maintained at a temperature of about 360-380 ° F (182-193 ° C). The molten foam mixture is extruded from a 12 inch (30.5 cm) wide coat hanger die maintained at 380 ° F. and brought to a temperature of about 130 ° F. (54 ° C.) located about 6 inches (15 cm) from the die exit. S-wrap (via a maintained three roll finishing roll stack)
S-wrap) and wound on a winder. For these examples, the winding speed used was chosen to provide only the orientation of the expanded polypropylene and approximately the nominal stretch in the machining or flow direction.

An improved extrusion die substantially as shown in FIG. 3 and having a ratio t ₁ / t ₂ = 1.2 and a ratio l ₁ / l ₂ = 3.5 was prepared in Examples 1-6 and Comparative Examples C-1 Used to extrude C-3 foam sheet. The foam sheet for each formulation is extruded under low and high shear conditions to demonstrate the mixing effect on cell distribution and uniformity. Low shear mixing was performed at a low extruder screw speed of 86 rpm and high shear mixing was performed at a high extruder speed of 120 rpm.

As shown below, the mechanical and thermal properties of the foam sheet samples were determined. All of the formulations described in Table I below are also Irga from Ciba Geigy.
Contains 0.08 wt% of nox168 stabilizer and 0.04 wt% of Irganox 1010 stabilizer. Examples 2 to 4
Contains 0.02 wt% of a synthetic talc salt KYOWA DHT-4A grade obtained from Mitsui to neutralize acid catalyst residues. The resin component of these compounds (residual for 100 wt%) is P
P-1 is a propylene homopolymer. All formulations are per 100 parts of formulation before extrusion
Bound with 0.5 pbw (active) of SAFORM FPE-50 blowing agent.

[0061]

[Table 1]

The presence of a nucleating agent as in Examples 1 to 6 or the absence of a nucleating agent as in Comparative Examples C-1 to C-3 does not affect the melting point Tm. The crystallization temperature Tc of the uncombined polypropylene used in these examples is 127 ° C. for PP-1. However, as seen in Comparative Examples C-1 to C-3, the addition of talc reduces the temperature to about 121 ° C. Therefore, the nucleating agents Nucl-1 and Nucl-2 act to eliminate the influence of talc on the crystallization temperature Tc. Nucl-2 also improves Tc. Examples 1 to 5 are compared with C-1 to C-4.

The sorbitol compounds described in the art as suitable network binders for nuclear crystallization in polyolefins appear to slightly improve the crystal melting temperature of the inventive foamable formulations based on polypropylene.

Table II below shows the determined densities and thermal conductivities for the extruded foamed sheet samples at low and high shear conditions for each of the formulations described above.

[0065]

[Table 2]

The effect of high shear mixing in the extruder is to increase the melting point, thus improving cell distribution and reducing average cell size. Comparing the density of foam produced at low shear conditions with the corresponding foam produced at high shear conditions generally reflects better insulation (reduced thermal conductivity) As will be appreciated, it will be apparent that high shear mixing conditions provide a low density foam having a more uniform cell distribution.

The mechanical properties of the low-shear and high-shear foam sheets of Examples 1 to 6 and Comparative Examples C-1 to C-3 were also determined. The tensile properties are outlined in Table III below. The samples were tested in the machine direction.

[0068]

[Table 3]

[0069]

Examples 7-12 In the following Examples 7-12, the formulations outlined in Table IV were used, as described in Examples 1-6, using a screw speed of 120 rpm to ensure good mixing. hand,
Mix and extrude. For extruding a foam sheet, it is substantially shown in FIG.
An extrusion die which is improved with a ratio t ₁ / t ₂ = 1.2 and the ratio l ₁ / l ₂ = 3.5 was used.

This formulation also contains 0.08 wt% of Irganox 168 stabilizer from Ciba Geigy and Irganox
Contains 1010 stabilizer 0.04wt%. The balance of the formulation (relative to 100 wt%) is the indicated resin component. The formulation was combined with 0.5 pbw (active) blowing agent per 100 parts of the formulation prior to extrusion.

[0071]

[Table 4]

It can be seen that not all blowing agents have obtained comparable results. The H-40E foaming agent (Example 12) showed a poor cell distribution and large
It can be seen that irregular, continuous and interconnected cells are provided. Examples 7-1
The foam sheet of Example 12 had a rough surface with voids, although the surface of the foam sheet of No. 2 had no noticeable bands. Clearly, these flaws
This is the result of using an ineffective coarse particle blowing agent. The cells of Examples 7 to 12 were observed by SEM on a cross-sectional view cut in the transverse direction. As a result, the cross-section appeared to be basically circular. When observing a cross section along the machining direction, these foam cells will appear to be enlarged along the flow direction.

The foamed sheet having a thermal conductivity of about 14 W / m ゜ K or less, preferably about 11 W / m ゜ K or less is used for food provision applications, particularly when serving hot or cold foods by serving. Particularly desirable for use in the manufacture of cups and similar articles. As a comparison, the thermal conductivity of a non-foamed extrusion stabilized PP-2 polypropylene sheet having a nominal thickness of 40 mils (1 mm) is 0.2 W / m ゜ K. The thermal conductivity of the stock used to make the paper cup is about 0.12 W / m ゜ K, and the thermal conductivity of the stock for the styrofoam cup is about 0.09 W / m ゜ K.

[0074]

Comparative Example C-4 For comparison, a foamed sheet was extruded using the foamable polypropylene composition of Example 11 shown in Table IV using a conventional die. Conventional extrusion dies are almost
It is as shown in. The foam sheet has an average thickness of 35 mils (0.9 mm) and an average density of 0.62 g / cm ³ .

The foamed sheet of Comparative Example C-4 was visually observed by SEM, and appeared to have a bad cell distribution. The surface of the foamed sheet was made of a commercially available non-regenerated polypropylene resin using a conventional die. There were bands running in the machine direction typically found on extruded foam sheets, visible defects with defects.

As noted in Table IV above, when observed by SEM, the surface appearance of the inventive foamed sheet of Example 11 appeared excellent with no observable surface voids. . Visual inspection showed that the foamed sheet of Example 11 had no visible bands and other significant surface defects.

Further comparing the surface appearance of various foamed sheet sections by determining the surface roughness and uniformity using each of the roughness parameters obtained from image analysis of a microphotograph of the sheet surface. Can also. Sheet sections suitable for evaluation are almost extruded sheets in Examples 10 and 11; representative sections of unacceptable foam sheets for comparison are those described in Comparative Example C-4. These were evaluated. Representative sections of the foam sheets outlined in Table V as Examples A-C were prepared by extruding a common polypropylene resin using conventional manufacturing methods as in Comparative Example C-4 and further compared. .

For evaluation, an area of about 5 mm × 16 mm on the sheet surface is visually observed and photographed by SEM. The test area was chosen to include the wavy lines (if they were present) along with the apparent surface roughness. The visual appearance evaluation was then determined by image analysis of 16 regions each 1 mm wide and 5 mm long selected to run parallel to the wavy lines. Fraction of the dark area (%
), The standard deviation (%) in the dark area for the 16 strips, and the average dark area (%) for the total area tested. The results of these evaluations are outlined in Table V.

The average roughness is related to the percentage of the dark area relative to the total area tested, and a high average roughness indicates the presence of many voids and depressions, ie, the surface where the irregularities appear.

Variations in average roughness between surface areas indicate a non-uniform distribution of cells, voids and depressions on the surface. For a completely non-uniform surface, whether uneven or smooth, the average roughness between the various surface areas will vary only slightly.

The standard deviation is related to the uniformity of the surface roughness and indirectly to the uniformity of the internal cell distribution. A low standard deviation indicates that the cells, voids, and depressions on the surface are more evenly distributed, indicating that the internal cell distribution is more uniform.

The criteria for evaluating and indexing the surface roughness and uniformity are shown in the table below.

[0083]

[Table 5]

[0084]

[Table 6]

A first characteristic of foamed sheets having an acceptable surface appearance is the uniformity of the surface roughness distribution. If the surface roughness is evenly distributed, the foamed polypropylene sheet will have a good visible appearance, whether as low as in Example 10 or as high as in Example 11. Will. Very weak wavy lines
This is a result of the fact that the surface defects are not so uniformly distributed as in Example A. The more uneven the distribution, the more pronounced the waveform, which has a detrimental effect on the surface appearance. See Example B and Comparative Example C-4. Conversely, when distributed in a very non-uniform manner, as in Example C, low surface roughness provides a sheet with a very undesirable surface appearance.

Thus, an acceptable foam sheet is considered to be a sheet that has a uniform distribution of surface roughness and reflects the overall uniformity of the internal cell distribution. For the foamed sheet of the present invention, the standard deviation in surface roughness is a uniform measurement, generally about
6.0% or less, more preferably about 5.0% or less, and most preferably about 4.0% or less.

Thus, the present invention relates to an improved polypropylene composition for use in extruded foamed sheet products, and more preferably, having a thickness of about 20 to about 80 mils (0.5 to 2 mm) and a density of about 0.4 to 0.4 mil. It relates to a rigid or semi-rigid foamed polypropylene sheet having a weight of 0.8 g / cm ³ . The rigid foamed polypropylene sheet of the present invention will have a significant improvement in surface appearance substantially free of banding and wavy markings commonly found in conventional rigid extruded foamed polypropylene. The present invention further general polypropylene comprises and from about 0.4 to about density of 0.8 g / cm ³ as defined herein, and less than about 6%, more preferably less than about 5.0%, most preferably May be characterized as relating to a rigid foamed polypropylene sheet having a uniform distribution of surface roughness, which may be defined as a standard deviation of average surface roughness lower than about 4.0%.

The invented method comprises forming a foamable composition comprising a polypropylene resin and a blowing agent,
Extruding from an improved coat hanger extrusion die. The improvement of this die is that it includes a die land having a hole that widens in the downstream direction to the exit opening of the die, and provides an expansion zone in the die land. The widening hole has a ratio of the exit opening height to the minimum height in the die land of about 2 to about 5, and the difference between the passage height at the die opening and the minimum height in the die land is about 0.004 to about 0.10. Inches (0.01
~ 0.25cm) in width. Generally, the difference between the length of the die land and the length of the widened or expanded zone is in the range of about 0.125 inches to about 0.75 inches (0.3-1.9 cm).

Thus, the present invention may be characterized as relating to an improved foam extrusion die as described and described herein. Although the present invention has been described and illustrated by the specific embodiments described herein, one of ordinary skill in the art would include a dispersed phase comprising a copolymer, for example, as disclosed in the art. It will be appreciated that various polypropylene homo- and copolymer resins, including impact-absorbing polypropylene resins based on isotactic polypropylene, are also useful. It should be noted that further modifications and diversification of the methods used herein for the production of foamed sheets will be readily apparent to those skilled in the field of resin formulation and manufacture and those skilled in extrusion molding. Would.
It will also be understood that such changes and diversification are within the scope of the invention as defined by the appended claims.

[Brief description of the drawings]

FIG. 1 is a partially transparent perspective view of a coat hanger type sheet extrusion die.

FIG. 2 is a cross-sectional view of a conventional polypropylene sheet extrusion die cut along the line AA of FIG.

FIG. 3 is a cross-sectional view of the improved sheet extrusion die of the present invention taken along line AA of FIG.

FIG. 4 is a cross-sectional view of yet another embodiment of the improved sheet extrusion die of the present invention taken along line AA of FIG.

FIG. 5 is a partially enlarged view showing details of a die land of the embodiment of FIG. 4;

[Procedure amendment]

[Submission date] March 21, 2001 (2001.3.21)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005] A number of methods for making expanded polypropylene have been disclosed and described in the art.
For example, U.S. Patent No. 5,18, JJPark et al., Which is incorporated herein by reference.
And the method disclosed in Japanese Patent No. 0,751 . Park et al.'S patent is generally around 0.0
Regarding extrusion of polypropylene to provide a foamed sheet of low density in the range of 4~0.40g / cm ^3.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0065

[Correction method] Change

[Correction contents]

[0065]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 5/523 C08K 5/523 C08L 23/10 C08L 23/10 // B29K 23:00 B29K 23:00 105 : 04 105: 04 B29L 7:00 B29L 7:00 (31) Priority claim number 60 / 128,173 (32) Priority date April 6, 1999 (1999.4.6) (33) Priority claim Country United States (US) (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW ), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC , LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW (72) Inventor Jacobi, Phil 30062, Marietta, Georgia, United States 4325 Granby Way 4325 (72) Inventor Novak, Mark Sea United States Georgia 30005, Alf Retta, Belmont Chase Coat 325 (72) Inventor Metathass, Constantin 30004, Georgia, USA, Al Faretta, Marker Lane 1070 (72) Inventor Choi-Fen, Ching, United States of America 30022, Al Faretta, Clen Cops, United States 415 (72) Inventor Mills, Ray O. 30075, Roswell, Highland Colony Drive, Georgia, USA 11795 (72) Inventor Fen, Dern, 30022, Georgia, USA, Al Faretta, Clen Cops 415 F-term (reference) ) 4F074 AA24 AB05 AC17 AC32 AC36 AD09 AD10 AD16 AG01 AG20 BA01 BA03 BA31 CA22 CA23 DA02 DA15 DA23 DA24 DA34 4F207 AA11A AA11B AB02 AB08 AB16 KA01 KA11 KL84 KM06 KM16 KW26 4J002 BB121 BB141 DJ0 137 DJ01 137 EG076 EQ018 EW046 FD017 FD206 FD328 GG01

Claims (10)

[Claims] 1. A crystallization nucleating agent having a melt flow rate of about 0.5 to about 30 g / 10 min and a crystallization nucleating agent of 0.05 to 0.5 wt%, a finely divided inert solid of 0.01 to 5 wt%, and a blowing agent of 0.1 to 25 wt%.
A foamable polymer composition comprising a polypropylene resin dispersed therein. 2. The foamable polymer composition according to claim 1, wherein the crystallization nucleating agent is sodium organic phosphate, sodium benzoate, and (a) an aromatic monocarboxylic acid or an aliphatic polycarboxylic acid. A composition comprising at least one nucleating agent selected from the group consisting of a mixture of an acid and (b) a silicate or an aluminosilicate of an alkali metal or an alkaline earth metal. 3. The foamable polymer composition of claim 1, wherein the finely divided inert solid is selected from the group consisting of talc, silicon dioxide, diatomaceous earth, kaolin and titanium dioxide. A composition comprising: 4. A rigid foamed polypropylene sheet having a density of 0.4 to 0.8 g / cm ³ obtained by foaming extrusion of the composition according to any one of claims 1 to 3. 5. A range of 0.4 to 0.8 g / cm ³ molded by thermoforming a rigid foamed polypropylene sheet extruded from the composition according to claim 1. Molded article comprising a foamed polypropylene resin having a density of 0.5 to 2 mm. 6. A substantially linear propylene polymer foam having an essentially monomodal molecular weight distribution and a melt flow rate of 0.5 to 30 g / 10 min, comprising from about 0.4 to 0.
A hard extruded sheet having a density of .8 g / cm ³ and a standard deviation of surface roughness of 6% or less. 7. A mold comprising a substantially linear propylene polymer foam having an essentially monomodal molecular weight distribution and a melt flow rate of 0.5 to 30 g / 10 min, with a standard deviation of surface roughness of 6% or less. Molded articles. 8. A device for extruding a foamed sheet from the foamable molten mass, the cavity, and a die having inlet and outlet openings of the height t ₁ of the second end portion of the first end portion, the inlet and A die land in fluid communication with the outlet opening, wherein the hole in the die land becomes wider along the minimum height t ₂ and the outlet opening along the extrusion axis of the die, the ratio of t ₁ / t ₂ Is in the range of about 2 to about 5. 9. A coat hanger die for extruding a foamed sheet from the foamable molten mass, the entrance and exit openings in fluid communication with a height t ₁ of the second end portion of the first end portion of the die First and second halves surrounding a die cavity having a coat hanger-shaped plenum, and upper and lower die lips at a second end defining a die land in fluid communication with the plenum and the outlet opening. When provided with a hole of the die land becomes wider as the lead to the outlet opening along a minimum height t ₂ and the second extrusion axis, the ratio of t ₁ / t ₂ is in the range of from about 2 to about 5 A coat hanger die characterized by the following. 10. A method of extruding a foamed sheet having an improved surface appearance, comprising: a die land and an outlet opening having a height t ₁ in fluid communication with the die land, wherein the holes in the die land have a minimum height t ₂ and along the extrusion axis of the die to form an expanded zone becomes wider as the lead to the outlet opening, through a coat hanger extrusion die in the range ratio is from about 2 to about 5 of t ₁ / t _2, a polypropylene resin and Extruding a foaming composition containing a foaming agent, forming a foamed polypropylene extrudate having a predetermined thickness, stretching the extruded product through a finishing roll to produce a foamed sheet, and taking out the foamed sheet. A method comprising: